Wykorzystanie markerów molekularnych i fenotypowych do identyfikacji genów odporności pszenicy na łamliwość źdźbła powodowaną przez Oculimacula yallundae i O. acuformis

Łamliwość źdźbła to jedna z ważniejszych chorób pszenicy uprawnej (Triticum aestivum L.) powodowana przez dwa grzyby patogeniczne Oculimacula yallundae i Oculimacula acuformis. Istnieje kilka źródeł odporności na ten patogen, lecz jak dotąd tylko dwa geny Pch1 i Pch2 zostały przniesione do pszenicy uprawnej i warunkują odporność. Wybranie najkorzystniejszych markerów molekularnych dla określenia obecności genów odporności na łamliwość źdźbła u pszenicy może poprawić skuteczność i dokładność przy wyborze genotypów odpornych na tę chorobę. Celem pracy było określenie efektywności markerów molekularnych i markera izoenzymatycznego dla genów Pch1 i Pch2 oraz wytypowanie genotypów pszenicy ozimej o podwyższonej odporności w odniesieniu do porażenia roślin w testach inokulacyjnych przeprowadzonych w fazie siewki oraz rośliny dojrzałej. Materiał badawczy stanowiło 159 linii hodowlanych pszenicy ozimej oraz pięć odmian kontrolnych: Artist, Kilimanjaro, Kometa, Patras i Rendezvous. Do identyfikacji genów odporności wykorzystano pięć markerów, trzy do identyfikacji genu Pch1 (EpD1b, XustSSR2001-7DL, Xorw1) oraz dwa dla genu Pch2 (Xcfa2040, Xwmc525). Biorąc pod uwagę analizę molekularną genów, wyniki inokulacji siewek oraz wyniki porażenia źdźbeł dojrzałych roślin, stwierdzono brak objawów porażenia źdźbeł u linii/odmian pszenicy ozimej, u których zidentyfikowano oba geny Pch1 i Pch2. Stwierdzono u nich również najniższe porażenie siewek. Najwyższy procent porażonych źdźbeł odnotowano u genotypów, gdzie nie stwierdzono genów Pch1 i Pch2. U tych genotypów zaobserwowano również najwyższe porażenie w teście siewkowym. Wykazano, że obecność genów Pch1 i Pch2 lub ich brak nie wpływała istotnie na plon ziarna oraz na masę tysiąca ziarniaków (MTZ). U genotypów z genami Pch1 i Pch2 stwierdzono nieznacznie wyższe wartości dla obu parametrów technologicznych.

Reaction of winter wheat cultivars to eyespot assessed visually and by real-time PCR

The reaction of twelve winter wheat cultivars frequently grown in the Czech Republic and twenty-five new breeding lines to inoculation with Oculimacula yallundae and Oculimacula acuformis was evaluated in small plot trials from 2017–2018. The assessment was carried out visually by symptoms and by a quantitative real-time polymerase chain reaction (qPCR). The aims of the study were to compare the results of both methods, to evaluate the effect of the resistance gene Pch1 to eyespot, and to select new breeding lines resistant to eyespot. The relationship between the eyespot symptoms and the pathogen DNA content in plant tissues followed a moderate linear regression. Low levels of eyespot were observed in the cultivars/lines possessing the resistance gene Pch1 (Annie, Hermann, Rebell, SG-S1215-14, SG-S1825-14, SG-S791-13) and also in the line SG-SU630-15. The qPCR method was able to detect low levels of the pathogens in the plant tissue and to distinguish two eyespot pathogens. O. acuformis was detected in very low concentrations in the inoculated plants compared with O. yallundae. The eyespot infection rate was significantly higher in 2017 than in the next agricultural season due to extremely dry and warm spring weather in 2018.

Resistance of winter wheat cultivars to eyespot and characterisation of causal agents of the disease

The reaction of ten winter wheat cultivars grown in the Czech Republic to inoculation with Oculimacula yallundae and Oculimacula acuformis was evaluated in a small plot trial. In a parallel field trial the natural occurrence of stem-base disease complex in six of the tested cultivars was assessed. Lower severity of eyespot (and/or stem-base diseases) was observed in cultivars possessing the resistance gene Pch1 (cvs Hermann, Annie, Princeps, Manager, and Rebell) in plots inoculated with Oculimacula spp. as well as in natural field conditions. A total of 468 wheat stem bases from the Czech Republic was screened by PCR to study the frequency of eyespot causal agents. The plants were colonised significantly more often by both species Oculimacula yallundae and O. acuformis together than separately.

Occurrence and Survival of Apothecia of the Eyespot Pathogens Oculimacula acuformis and O. yallundae on Wheat Stubble in the U.S. Pacific Northwest

Eyespot is a chronic disease of wheat caused by Oculimacula yallundae and O. acuformis that results in premature ripening of grain, lodging, and reduced grain yield. Discovery of the sexual stage of these Oculimacula spp. in the Pacific Northwest (PNW) of the United States is relatively recent and the role of apothecia in the epidemiology of eyespot is unclear. Our goals were to determine whether and when apothecia of these Oculimacula spp. are found in the PNW, and monitor their ability to survive over summer and over winter. Seventy-three harvested commercial wheat fields in Idaho, Oregon, and Washington were surveyed for apothecia during spring and fall 2012 and spring 2013. Apothecia of both species were found in both spring and fall in 19% of fields. Apothecia survived on straw placed on the soil surface over the summer but not the winter. This is the first report of O. yallundae apothecia in commercial wheat fields in the PNW. Occurrence of apothecia in spring and fall demonstrates that sexual reproduction of both species occurs regularly in the PNW and at a time when ascospores could serve as primary inoculum for infection of winter wheat. Results of this study are consistent with previous population genetic studies that found high genotypic diversity of both eyespot pathogens in winter wheat fields and provides a baseline for understanding the influence of sexual reproduction on population dynamics and genetics of both pathogens.

Chlorophyll fluorescence parameters allow the rapid detection and differentiation of plant responses in three different wheat pathosystems

The present study was undertaken to identify chlorophyll fluorescence (CF) parameters that can quantify changes in PSII associated with plant responses in three different wheat pathosystems of foliar, stem-base and ear diseases. The pathosystems included powdery mildew caused by Blumeria graminis, eyespot caused by Oculimacula yallundae or Oculimacula acuformis and Fusarium head blight (FHB) caused by Fusarium culmorum, F. avenaceum or F. langsethiae. Fast CF transients (OJIP) were analysed with the JIP-test to determine changes in PSII photochemistry. Measurements on asymptomatic leaves showed that electron transport related parameters (ETo/RC, ψo and ϕEo) were important to identify varietal differences in resistance to powdery mildew during early stages of infection. The same parameters also allowed differentiation between F. langsethiae and other Fusarium spp. Where infections were caused by the necrotrophic pathogens, Oculimacula spp., F. culmorum or F. avenaceum, changes related to maximum efficiency of PSII photochemistry (Fvʹ/Fmʹ) as well as flux of dissipated (DIo/RC), trapped (TRo/RC), or absorbed (ABS/RC) energy per active reaction centers were significant in detecting biotic stress and the effectiveness of fungicide treatment for disease control. Our results demonstrated that Fvʹ/Fmʹ correlated significantly with visual disease and pathogen DNA of different wheat pathosystems. OJIP was shown as a sensitive technique that can be explored as diagnostic tool in future crop disease management and varietal breeding programs.

Identifying New Sources of Resistance to Eyespot of Wheat in Aegilops longissima

Eyespot, caused by Oculimacula yallundae and O. acuformis, is an economically important disease of wheat. Currently, two eyespot resistance genes, Pch1 and Pch2, are used in wheat breeding programs but neither provides complete control or prevents yield loss. Aegilops longissima is a distant relative of wheat and proven donor of genes useful for wheat improvement, including disease resistance. Forty A. longissima accessions and 83 A. longissima chromosome addition or substitution lines were evaluated for resistance to eyespot. Among the 40 accessions tested, 43% were resistant to O. yallundae, 48% were resistant to O. acuformis, and 33% were resistant to both. Addition or substitution lines containing chromosomes 1S1, 2S1, 5S1, and 7S1, and a 4S17S1 translocation were resistant to O. yallundae. Chromosomes 1S1, 2S1, 4S1, and 5S1 contributed to resistance to O. acuformis more than others. Chromosomes 1S1, 2S1, 5S1, and 7S1 provided resistance to both pathogens. This is the first report of eyespot resistance in A. longissima. These results provide evidence that genetic control of eyespot resistance is present on multiple chromosomes of the S1 genome. This research demonstrates that A. longissima is a potential new source of eyespot resistance genes that could broaden the genetic diversity for wheat improvement.